Telecommunications systems are carrying increasing amounts of information, both in the long distance network as well as in metropolitan and local area networks. At present data traffic is growing much faster than voice traffic, and will include high bandwidth video signals. In addition to the requirement for equipment to carry increasing amounts of telecommunications traffic there is a need to bring this information from the long distance network to businesses and to locations where it can be distributed to residences over access networks.
The equipment which has been developed to carry large amounts of telecommunications traffic includes fiber optic transport equipment which can carry high-speed telecommunications traffic. The data rates on fiber optic systems can range from millions of bits per second (Mb/s) to billions of bits per second (Gb/s). In addition, multiple wavelengths of light can be carried on an optical fiber using Wavelength Division Multiplexing (WDM) techniques.
The ability to carry large amounts of telecommunications traffic on an optical fiber solves the long-distance point-to-point transport problem, but does not address the issue of how to add and remove traffic from the high-speed data stream. Equipment for adding and removing traffic has been developed and is referred to as “add-drop” multiplexing equipment.
Traditional designs for add-drop multiplexers are based on the use of multiple interface cards which receive high speed data streams, create a time division multiplex signal containing the multiple data streams, and route the time division multiplex signal to a cross-connect unit which can disassemble the data streams, remove or insert particular data streams, and send the signal to another interface card for transmission back into the networks. By aggregating the multiple data streams into a time division multiplexed data signal, the data rate of the time division multiplexed signal is by definition several times the rate of the maximum data rate supported by the interface cards.
An advanced system for providing, among other things, the above mentioned functionality including routing and cross connecting circuits is described in detail in the co-pending application Ser. No. 09/274,078 which is incorporated herein by reference. In that system, cross-connects can groom traffic in STS-1 or VT1.5 payload increments to any port on any card. The cross connects are a means for directing and re-directing traffic in the network. This maximizes bandwidth efficiency by making it possible to groom SONET traffic in STS-1 or VT1.5 increments. FIGS. 1, 2, and 3 show various aspects of the flexible cross connect system as described in application Ser. No. 09/274,078. FIG. 1 illustrates a functional diagram of the flexible cross connect system; FIG. 2 illustrates communications channels between elements of the flexible cross connect system; FIG. 3 illustrates the software architecture of the control system for the flexible cross connect system. In a preferred embodiment XC unit 120 supports all VT 1.5 through STS-192 applications. Grooming and cross-connect functionality is well known to those skilled in that art.
A SONET network typically comprises multiple network elements, or nodes, interconnected by physical media (e.g., optical fiber links). When used herein, the term SONET is meant to include not only SONET, but also Synchronous Digital Hierarchy (SDH) networks and systems and other equivalents. Furthermore, when used herein, the term STS is meant to include not only SONET Synchronous Transport Signals (STS), but SDH Synchronous Transport Modules (STMs) and other equivalents, and the term Virtual Tributary (VT) is meant to include not only SONET VT, but SDH Virtual Container (VC) and other equivalents. In order to route communication signals in the network from one node, a source node, to another node, a destination node, it is necessary to establish a circuit between the source and destination nodes. Establishing such a circuit entails provisioning a path, through the network, from the source node to the destination node. This path will typically traverse one or more other intervening nodes. A network manager (i.e., a user) typically is able to view, via a Network Management System's (NMS) graphical user interface (GUI), the network, and is able manually route a circuit through the intervening nodes. Alternatively, a routing algorithm can be used to automatically find one or more of such paths between two nodes. Routing algorithms such as Djikstra's SPT algorithm are well known to those skilled in the art. Advanced algorithms such as those described in the copending application Ser. No. 09/487,366, are utilized in the present invention to identify parameterized least cost paths.
Generally, in order to route (and switch) a VT circuit through the network while traversing a particular NE, the NE must provide VT cross-connect functionality. Individual network elements (NEs) may provide different levels of service regarding cross-connect functionality. It is not uncommon in art, for example, for some NE not to support VT cross connections at all. Alternatively, other NE may provide only a limited number of VT cross connects (XC). VT cross-connects are thus a precious resource in a network and within elements that provide such functionality, and the number of VT circuits that can be routed through a typical NE is typically relatively low (e.g., 1/10). In order to route (i.e. cross-connect) a VT circuit through various NEs in the network therefore, each network element would have to support VT cross-connects, that is, each NE would have to provide VT cross connect functionality. As previously stated, prior and current art NE either do not provide such VT cross connect functionality or they provide limited functionality (i.e. the number of VT cross connects in a NE, and thus the number of VT circuits which can be routed through the NE, are limited). This lack of available VT cross connects poses restrictions on routing VT circuits. In one case, a network path cannot be found for a VT circuit between two nodes because one or more intervening nodes in each possible path does not support or provide VT cross connects. In this case, it would not be possible to route a VT circuit between the two nodes.
In another case, there may exist one or more paths between the two nodes in which each intervening node supports VT cross connects, but this path may not be the shortest or least cost path. As stated above, routing circuits via a least cost path is desirable for network bandwidth optimization. Thus, although a VT circuit can be routed between the two nodes, it will not be the optimal, least cost, path. In another example, perhaps a least cost path can be found on which to route the VT circuits (i.e. the intervening nodes support the VT XCs), but an alternative path supporting VT XC required for path protection, cannot be found. This scenario would prohibit the provisioning of a least cost path protected VT circuit.
In summary, because provisioning VT circuits typically entails provisioning VT cross connects (XC) on intermediate nodes, routing VT circuits on such a network may be difficult or impossible due to a limited capacity or lack of available VT XC. Furthermore, although a path may be found on which to route the VT circuit, this path may not be the shortest path or may not be protectable, and would thus be sub-optimal.
Based on the foregoing description, there is a need for a method and system for enhancing the network topology on which VT circuits can be routed and for optimally routing and provisioning VT circuits through NE that provide limited or no support for cross connecting VT circuits.